Method for controlling valves during the stop of an engine having a variable event valvetrain

ABSTRACT

A method for controlling valves during an engine stop is presented. The valves are controlled in a manner that can quiet the engine during a stop. In addition, the valves may be selectively controlled to direct the contents of the cylinder in a desired direction so that engine emissions may be reduced.

The present application is a continuation of U.S. patent applicationSer. No. 11/397,993 filed Apr. 5, 2006, the entire contents of which isincorporated herein by reference in their entirety.

FIELD

The present description relates to a method for controlling valves of aninternal combustion engine during engine stop conditions.

BACKGROUND

Fuel efficiency and performance of an internal combustion engine may beimproved by varying the timing of intake and/or exhaust valves. One typeof variable event valvetrain uses electrically actuated valves tocontrol flow through a cylinder. Electrically actuated valves do nothave to be actuated in synchronization with the engine crankshaft. Thatis, the opening and closing timing of the valves may be varied, withinsome limits, as desired. One electrically actuated valve design balancesan actuator armature between force opposing springs. When the actuatoris not powered the balanced spring forces position the armature actuatedvalve in a neutral position. The neutral position locates the cylindervalve at a partially open position that potentially allows flow into orout of the cylinder. One method to stop an engine cuts power flowing tothe valves and stops fuel from flowing to the cylinders upon receivingan engine stop request. As a result, the valves are released to theirneutral position and the engine is stopped.

The above-mentioned method can also have several disadvantages. Namely,cutting power to a valve after a request to stop or after a stop cancause gases to enter or exit a cylinder depending on the pressuredifferential across the valve. This can produce an undesirable poppingsound as the valve releases from a closed position and seeks the neutralequilibrium position. Furthermore, by cutting power to the valves littleif any control is provided over where or when the cylinder gases exit orenter the cylinder. For example, for an engine having electricallyactuated intake and exhaust valves, some cylinders may be at a pressurebelow atmospheric pressure while others may be at a pressure that isabove atmospheric pressure. When the valves are released some of thecylinder contents may be expanded to the exhaust while others may beexpanded to the intake manifold. This may increase engine emissionssince some cylinder contents may travel through the intake manifoldbefore being vented to atmosphere, for example.

The inventor herein has recognized the above-mentioned disadvantages andhas developed a method to control engine valves during stopping andstarting that offers substantial improvements.

SUMMARY

One example approach to overcome at least some of the disadvantages ofprior approaches includes a method for stopping an engine having avariable event valvetrain, the method comprising: stopping said engine;and adjusting the current flow to at least a valve actuator to controlthe rate a valve is opened by said valve actuator. This method can beused to reduce the above-mentioned limitations of the prior artapproaches.

By controlling the rate that valves are opened after an engine stop thenoise caused by gases passing the valves when they are released may bereduced. The position of a cylinder valve can be controlled by adjustingthe amount of current sourced to the valve closing magnet. In otherwords, current flowing to the closing electro-magnet produces a magneticfield force that can counter the valve opening spring. Balancing orcountering the spring force with a magnetic force allows the valve to beopened at a reduced rate and lowers the audible noise produced by gasesentering or exiting a cylinder.

In another aspect of the description, cylinder contents may be allowedto first flow to or from the intake manifold or exhaust manifold, asdesired. By opening selected valves first, in a desired order, thecontents of a specific cylinder may be directed toward the intakemanifold or the exhaust manifold as desired. For example, if a selectedcylinder contains pressurized exhaust constituents the cylinder exhaustvalve may be opened at a controlled rate so that the pressurized exhaustgases flow from the cylinder to the exhaust system and to an aftertreatment device. This can increase the possibility of treating theexhaust gases so that less undesirable emissions escape to theatmosphere. On the other hand, if the cylinder is in a state of vacuumthe intake valve may be opened at a controlled rate so that gases in theintake manifold may be drawn into the cylinder where they may have alower chance of escaping to the atmosphere.

The present description thus provides several advantages. Namely, themethod can reduce the audible noise that may be produced when a valve isallowed to go to the neutral or low energy use state. Further, gases maybe directed to or from a cylinder so that engine emissions may bereduced. Further still, different groups of valves may be opened atdifferent times and/or at different rates so that power consumption maybe reduced during a quiet engine stop.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings,wherein:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 a is a schematic diagram of an example turbo charged engineconfiguration;

FIG. 2 b is a schematic diagram of an alternate example turbo chargedengine configuration;

FIG. 3 is a schematic of an electrically actuated poppet valve;

FIG. 4 is a flow chart of an example engine shutdown strategy;

FIG. 5 is a flow chart of an example engine starting strategy;

FIG. 6 is an example valve sequence during engine shutdown and start;

FIG. 7 is an alternate example valve sequence during engine shutdown andstart;

FIG. 8 is an alternate example valve sequence during engine shutdown andstart;

FIG. 9 is a flow chart of a cylinder deactivation strategy for an enginehaving two turbo chargers;

FIG. 10 is a flow chart of a cylinder reactivation strategy for anengine having two turbo chargers;

FIG. 11 is an alternative flow chart of a cylinder deactivation strategyfor an engine having two turbo chargers;

FIG. 12 is an alternative flow chart of a cylinder reactivation strategyfor an engine having two turbo chargers;

FIG. 13 is an example plot of signals of interest during a simulatedcylinder deactivation sequence;

FIG. 14 is an example plot of signals of interest during a simulatedcylinder reactivation sequence;

FIG. 15 is an example flow chart of valve control while a vehicle istransitioned in “accessory” mode;

FIG. 16 is an example plot of valve positions of interest for a vehiclethat transitions between stop mode and “accessory” mode;

FIG. 17 is a block diagram of an example strategy to control a turbocharge engine having electrically actuated valves;

FIG. 18 a is an example plot of signals of interest during an increasingtorque request of a turbo charged engine having a variable eventvalvetrain;

FIG. 18 b is another example plot of signals of interest during anincreasing torque request of a turbo charged engine having a variableevent valvetrain;

FIG. 19 is a flow chart of a valve release strategy during an enginestop; and

FIG. 20 is a plot of valve position during an example valve release atengine stop.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is knowncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 an exhaust valve 54. Each intake and exhaustvalve is operated by an electromechanically controlled valve coil andarmature assembly 53. Alternatively, the intake 52 or exhaust 54 valvemay be mechanically actuated. Armature temperature is determined bytemperature sensor 51. Valve position is determined by position sensor50. Valve position may be determined by linear variable displacement,discrete, or optical transducers or from actuator current measurements.In an alternative example, each valve actuator for valves 52 and 54 hasa position sensor and a temperature sensor. In yet another alternativeexample, armature temperature may be determined from actuator powerconsumption since resistive losses can scale with temperature.

Intake manifold 44 is also shown having fuel injector 66 coupled theretofor delivering liquid fuel in proportion to the pulse width of signalFPW from controller 12. Fuel is delivered to fuel injector 66 by fuelsystem (not shown) including a fuel tank, fuel pump, and fuel rail (notshown). Alternatively, the engine may be configured such that the fuelis injected directly into the engine cylinder, which is known to thoseskilled in the art as direct injection.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to controller 12. UniversalExhaust Gas Oxygen (UEGO) sensor 76 is shown coupled to exhaust manifold48 upstream of catalytic converter 70. Alternatively, a two-stateexhaust gas oxygen sensor may be substituted for UEGO sensor 76.Two-state exhaust gas oxygen sensor 98 is shown coupled to exhaustmanifold 48 downstream of catalytic converter 70. Alternatively, sensor98 can also be a UEGO sensor. Catalytic converter temperature ismeasured by temperature sensor 77, and/or estimated based on operatingconditions such as engine speed, load, air temperature, enginetemperature, and/or airflow, or combinations thereof.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Turbo charger 49 is shown in communication with exhaust manifold 48 andintake manifold 44. Fresh air may be inducted past throttle body 125,compressed by turbo charger compressor 46, and directed to intakemanifold 44. Alternatively, throttle body 125 may be located downstreamof turbo charger compressor 46. If the throttle body is locateddownstream of the compressor, pressure and temperature transducers maybe installed in the intake manifold as well as between the compressorand the throttle (i.e., boost pressure and temperature).

Turbo charger turbine 43 is connected to turbo charger compressor 46 byshaft 47. During operation exhaust gases can flow from exhaust manifold48 to turbo charger 49, where expanding exhaust gases can rotate exhaustturbine 43 and compressor 46. Exhaust gases are directed from turbine 43to catalyst 70 for processing. Turbo charger efficiency may be adjustedby varying the vane position actuator 45 of the variable geometry turbocharger. Alternatively, the turbo charger may be a waste gate type ofturbo charger.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, andread-only-memory 106, random-access-memory 108, 110 Keep-alive-memory,and a conventional data bus. Controller 12 is shown receiving varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to water jacket 114; a position sensor119 coupled to an accelerator pedal; a measurement of engine manifoldpressure (MAP) from pressure sensor 122 coupled to intake manifold 44; ameasurement (ACT) of engine air amount temperature or manifoldtemperature from temperature sensor 117; and engine position from a Halleffect sensor 118 sensing crankshaft 40 position. In a preferred aspectof the present description, engine position sensor 118 produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined. Thecontroller may determine the amount of overlap between intake andexhaust valves as well as fuel timing, spark timing, and throttleposition.

The engine described in FIG. 1 may be the primary means of generatingmotive force in a vehicle or it may be part of a vehicle having morethan one means for generating motive force, a hybrid vehicle forexample. The engine may generate wheel torque in conjunction with anelectric motor when in a hybrid configuration. Alternatively, the enginemay generate wheel torque in conjunction with a hydraulic motor. Thus,there are many configurations whereby features of the presentdescription may be used to advantage.

Referring now to FIG. 2 a, a schematic of a turbo charged engineconfiguration is shown. The figure illustrates a six cylinder enginehaving two cylinder banks, typically referred to as a V6 engine.Cylinders 216, 218, and 220 comprise a first cylinder bank and cylinders210, 212, and 214 comprise the second cylinder bank. The first cylinderbank is shown in communication with a first intake manifold 220. Intakemanifold 220 is shown in communication with ambient air via throttle 250and turbo charger 201. Throttle 250 may be electrically or mechanicallyactuated. Turbo charger 201 may be a variable geometry or waste gatetype and compresses fresh air via compressor 236 which is driven byexhaust gases working on turbine 234. Alternatively, turbo charger 201may be driven by an electric motor. Exhaust gases exit cylinder 216,218, and 220 and are communicated to turbine 234 via exhaust manifold232. Flow through cylinder 216 is controlled by variably actuated intakevalve 240 and/or variable actuated exhaust valve 244. Alternatively, theengine may be configured with variably actuated intake valves and fixedtiming exhaust valves. Variably actuated intake and/or exhaust valvesmay be actuated by electrical, hydraulic, pneumatic, or mechanicalmechanisms. Intake valve 240 regulates flow from intake manifold 220into cylinder 216. Exhaust valve 244 regulates flow from cylinder 216 toexhaust manifold 232. Cylinders 218, 220, 210, 212, and 214 areconfigured in the same manner as cylinder 216. In addition, the secondcylinder bank comprised of cylinders 210, 212, and 214 is essentially amirror image of the first cylinder bank. That is, intake manifold 222 isin communication with the second cylinder bank via intake valves and isalso in communication with throttle 252 and with the compressor 237 ofturbo charger 203. Exhaust manifold 230 is in communication with thesecond cylinder bank via exhaust valves and is also in communicationwith the turbine 235 of turbo charger 203. Note that the size andperformance characteristics of the first cylinder bank components do nothave to match the size and performance characteristics of the secondcylinder bank. For example, turbo charger 201 may be capable ofproducing 20% more flow than that which may be produced by turbo charger203, if desired. Also note that it is possible to extend thisconfiguration to four, eight, ten, and twelve cylinder engines.

The turbo charger configuration shown in FIG. 2 a allows separatecontrol of throttles 250 and 252. It also allows separate control ofintake valves, exhaust valves, spark ignition, fuel delivery, and turbocharges between the first and second cylinder banks since the air pathsof the banks are independent of each other. Therefore, the cylinders ofthe first and second cylinder banks may operate with different cylinderair charge amounts. Further, since the valves may be variably actuatedone of the cylinder banks may be deactivated (i.e., producing little orno positive torque) while the other cylinder bank continues to operateso that the engine efficiency may be increased.

Note that the manifold/throttle/valve configuration shown in FIG. 2A isnot meant to limit or narrow the scope or breadth of this description.The cylinders of the respective banks form cylinder groups that areselected so that the engine will fire evenly (i.e., with substantiallythe same crankshaft angle distance between combustion event) while oneof the cylinder groups is deactivated. Therefore, in other examples, therespective intake manifolds may be configured such that they span bothcylinder banks. Furthermore, a cylinder group may be comprised ofcylinders from one or more cylinder banks.

Referring now to FIG. 2 b, a schematic of an alternate turbo chargeengine configuration is shown. The figure illustrates a six cylinderengine having two cylinder banks. Cylinders 286, 288, and 290 comprise afirst cylinder bank and cylinders 280, 282, and 284 comprise the secondcylinder bank. The first cylinder bank and the second cylinder banks areshown in communication with intake manifold 276. Intake manifold 276 isshown in communication with ambient air via throttle 278 and turbochargers 260 and 262. Alternatively, a throttle may be provided tocontrol air flow between each turbo charger and the intake manifold.Throttle 278 may be electrically or mechanically actuated. Turbochargers 260 and 262 may be a variable geometry or waste gate type andcompress fresh air via compressor 296 and 297 which are driven byexhaust gases working on turbines 294 and 295. Exhaust gases exitcylinder 286, 288, and 290 and are communicated to turbine 294 viaexhaust manifold 292. Flow through cylinder 286 is controlled byvariably actuated intake valve 270 and/or variable actuated exhaustvalve 274. Variably actuated intake and/or exhaust valves may beactuated by electrical, hydraulic, or mechanical mechanisms. Intakevalve 270 regulates flow from intake manifold 276 into cylinder 286.Exhaust valve 274 regulates flow from cylinder 286 to exhaust manifold292. Cylinders 280, 282, 284, 288, and 290 are configured in the samemanner as cylinder 286. Note that the size and performancecharacteristics of the first cylinder bank components do not have tomatch the size and performance characteristics of the second cylinderbank. For example, turbo charger 260 may be capable of producing 20%more flow than that which may be produced by turbo charger 262, ifdesired. Also note that it is possible to extend this configuration tofour, eight, ten, and twelve cylinder engines.

The turbo charger configuration shown in FIG. 2 b has a single throttleand the intake air path is shared between the two cylinder banks. Theintake valves, exhaust valves, spark ignition, fuel delivery, and turbocharges may be separately controlled, but this configuration sharescommon intake manifold pressure between the cylinder banks. Since thevalves may be variably actuated this configuration also allows one ofthe cylinder banks to be deactivated (i.e., producing little or nopositive torque by mechanically or electrically closing intake and/orexhaust valves, for example) while the other cylinder bank continues tooperate. However, changes in the valve timing of one cylinder bank mayinfluence the torque produced in the other cylinder bank. Consequently,a more complex valve control algorithm may be used to control valvetiming during cylinder deactivation when this configuration is usedinstead of the configuration shown in FIG. 2 a. In addition, a valve orthrottle may be necessary between the deactivated cylinder bank turbocharger and the intake system to prevent reverse flow through thedeactivated turbo charger.

Referring now to FIG. 3, a schematic of an example electrically actuatedvalve is shown. The valve actuator is shown in a de-energized state(i.e., no electrical current is being supplied to the valve actuatorcoils). The electromechanical valve apparatus is comprised of anarmature assembly and a valve assembly. The armature assembly iscomprised of an armature return spring 301, a valve closing coil 305, avalve opening coil 309, an armature plate 307, a valve displacementtransducer 317, and an armature stem 303. When the valve coils are notenergized the armature return spring 301 opposes the valve return spring311, valve stem 313 and armature stem 303 are in contact with oneanother, and the armature plate 307 is essentially centered betweenopening coil 309 and closing coil 305. This allows the valve head 315 toassume a partially open state with respect to the port 319. When thearmature is in the fully open position the armature plate 307 is incontact with the opening coil magnetic pole face 326. When the armatureis in the fully closed position the armature plate 307 is in contactwith the closing coil magnetic pole face 324.

In one embodiment, armature plate 307 includes permanent magnets. Inanother embodiment, armature plate 307 does not include permanentmagnets. Permanent magnets may be used to reduce valve actuator currentbecause the permanent magnet can hold the valve in a closed position inthe absence of a holding current, at least during some conditions.

As one alternative, an electrical valve actuator may be constructed of asingle coil combined with a two plate armature. In another alternative,the valve actuator may employ a lever mechanism between the actuatorarmature and the valve stem. This design may reduce power consumption insome circumstances since mechanical advantage of the lever may reducethe amount of current for valve opening and closing. The valve lift,duration, and timing methods described herein may also be extended tothis and other actuator designs since actuator designs are not intendedto limit the scope of this description.

Referring now to FIG. 4, a flow chart of an example engine shut-downstrategy is shown. In step 402, the routine determines if there has beena request to stop the engine. The request to stop may come from anoperator switch or from a system controller of a hybrid vehicle, forexample. If there is a request to stop the engine the routine proceedsto step 404. If not, the routine proceeds to exit.

In step 404, the routine evaluates a series of status registers thatcontain an indication of the current stroke of each cylinder (e.g.,power stroke, exhaust stroke, intake stroke, etc.) to determine theshutdown process for each cylinder, or alternatively for selectedcylinders. Valves in cylinders that contain a non-combusted air-fuelmixture may be allowed to continue the current cylinder cycle so thatthe air-fuel mixture may be combusted before holding selected valves inthe closed position. Valves in cylinders containing air without fuel maybe deactivated (i.e., one or more selected valves are held in the closedposition and combustion is inhibited) so that the shutdown time isshortened. Valves in cylinders containing exhaust gases may becontrolled to trap or expel the residual exhaust gas mixture and thenone or more valves may be held in a closed position after the exhaust isexpelled or directly after the request for shutdown is received so thatexhaust gases are trapped.

Alternative methods are also possible to shutdown one or more cylinders,for example, after a request to stop the engine, for one or morecylinders holding an uncombusted air-fuel mixture, combustion may beinhibited by deactivating the ignition and holding intake and exhaustvalves closed so that the uncombusted air-fuel mixture remains in thecylinder which may enable the mixture to be used during a subsequentrestart. Further, in another alternative, each cylinder or selectedcylinders may add one or more additional combustion cycles to any of theabove-mentioned cylinder deactivation sequences so that a fuel puddlereduction strategy may be executed. For example, for a cylinder in apower stroke during an engine stop request, the valves can be controlledsuch that the cylinder completes the current cycle and then the valvetiming may be adjusted before an additional cylinder cycle is completed.One or more valves may be set to the closed position during theadditional cylinder cycle so that flow through the cylinder is reduced.

Fuel flow to cylinders during a cylinder deactivation and/or engine stoprequest can also be controlled in a variety of ways. For port fuelinjected engines fuel flow to a cylinder may be stopped immediatelyafter a request to stop the engine or after a predetermined number ofintake events of the respective cylinder, for example. If the fuel flowis stopped immediately then the valve timing may be adjusted so that theair and fuel match the desired cylinder air-fuel ratio. Alternatively,fuel flow and valve timing adjustments may be made over a predeterminednumber of cylinder induction events so that fuel puddles may be drawninto the cylinder before combustion is stopped. For fuel directlyinjected into cylinders, fuel flow may be stopped immediately after therequest to stop, after a combustion event in the cylinder, or after alast induction event for the cylinder. Since the fuel flow is directlyinjected into the cylinder the valves may be closed partially through aninduction event while the desired cylinder air-fuel ratio is maintained.Fuel may be injected by direct injection systems while the intake valveis open or after the intake valve has closed. The routine proceeds tostep 406.

In step 406, selected valves may be held in a closed position as theengine decelerates and stops. Valves of a variable event valvetrain maybe controlled in a flexible manner that goes beyond fixed four strokevalve timing. This allows the valves to be uniquely controlled so thatengine performance and emissions may be improved. By closing selectedvalves during engine shutdown and/or during engine stop, gas flowthrough the engine and exhaust system may be reduced. Specifically,cylinder valves may be used to control oxygen flow into and exhaust gasflow out of the engine and exhaust system. Furthermore, holding one ormore cylinder valves closed may reduce the flow of evaporative emissions(e.g., hydrocarbons) from the engine and exhaust system. In addition,holding one or more cylinder valves closed can provide a better seal tothe engine and exhaust system than a closed throttle or throttle bypassvalve since throttles generally do not assume a fully closed positionduring engine stop. For example, typically, a throttle has a minimumopening amount so that the engine can idle if throttle degradationoccurs. In contrast, a cylinder valve may be set to a closed position sothat nearly all flow through a cylinder is inhibited.

Continuing with step 406, selected valves operating in cylinders may becommanded to a closed position depending on the position of the engineand stroke of the cylinder. In one example, selected valves in cylindersthat are between intake strokes during an engine stop request may beheld in a closed position as the engine decelerates to a stop and whilethe engine is in the stopped position. For example, if a request to stopthe engine occurs during the compression stroke of a certain cylinderthen the intake valves of that cylinder may be held closed after therequest to stop. The intake valves may be held closed as the enginedecelerates and then for at least a portion of the engine stop period.During a subsequent engine restart the intake valves may be commanded tothe open position and/or to open based on a four stroke cycle, forexample. During an engine shutdown where intake valves are held closed,the exhaust valves may be commanded to retain a predetermined schedule(e.g., four, six, or two stroke) or they may be commanded to an open orclosed position. In yet another alternative, during an engine shutdown,the intake valves are held closed and the cylinder exhaust valves may beheld closed after the combusted air-fuel mixture is exhausted from thecylinder. In this way, the exhaust valves may be commanded closed, open,deactivated (e.g., the neutral position of an electrically actuatedvalve), or they may be operated based on engine position so that engineemissions and pumping work may be controlled in a desired manner.Furthermore, since the intake valves are held closed, operation of theexhaust valves has little effect on flow from the intake side of thecylinder to exhaust side of the cylinder.

The type of fuel delivery system can also influence the manner andsequence of intake valves during an engine shutdown/stop where it may bedesirable to hold intake valves closed. For example, for a port fuelinjected cylinder the intake valve may be held closed after the intakeevent is completed and retained in a closed position until the engine isrestarted or until a specific time amount or condition has occurred. Bycompleting the intake event it may be possible to better control thecylinder air-fuel ratio after the request to stop the engine and/orcylinder because it may be simpler to determine the amount of fuel thatwill enter the cylinder from the injector and/or from any fuel puddlethat may have accumulated in the intake manifold.

On the other hand, if a request to stop the engine occurs during theintake stroke of a cylinder having fuel directly injected into thecylinder then the intake valve may be closed early. Since the engine isabout to be stopped, fuel may be matched to the short duration inductionevent so that a stoichiometric air-fuel mixture is produced.Consequently, fuel can be conserved (by lowering the fuel amount tomatch the reduced air charge) while maintaining a stoichiometricair-fuel. This is possible since fuel delivery to a directly injectedcylinder can be updated after the intake valve closes, at least undersome conditions. Alternatively, during early intake valve closing, fuelflow to a directly injected cylinder may be inhibited so that thecylinder shutdown is earlier. That is, a partial air charge may beinducted followed by holding the intake valves closed and trapping thepartial air charge, for example. Thus, a variable event valvetraincoupled with direct injection can provide additional benefits such asreduced fuel consumption and improved emissions during an engineshutdown. These benefits may be especially useful in applications wherethe engine is frequently stopped and restarted, sometimes referred to asstop-start applications.

As an alternative to holding intake valves closed after a request tostop an engine, exhaust valves may be held closed after the request tostop the engine. However, in some circumstances it may be desirable toexhaust any combusted gases remaining in the cylinder prior tocommanding the exhaust valves to a closed position since evacuatingexhaust gas from the cylinder may better prepare the cylinder for asubsequent restart. For example, if a request to stop the engine occursduring the compression stroke of a certain cylinder then the exhaustvalves may be held closed after a last air-fuel mixture (i.e., anair-fuel mixture that is inducted prior to or during the engine stoprequest) has been combusted and exhausted from a cylinder. In thisexample the intake valves may be held closed after the last combustionevent or they may be opened to periodically to regulate the amount ofair in the cylinder. Alternatively, the intake valves may continue tooperate in a predetermined manner (e.g., four, six, or two stroke basis)or they may be set to an open or neutral position. In this example, flowthrough the cylinder is limited since the exhaust valves of the cylinderare closed.

In some circumstance it may be beneficial to combust and exhaust a lastair-fuel mixture and then trap a known volume of air in the cylinder. Bytrapping a known amount of air in the cylinder and injecting fuel intothe cylinder for a subsequent restart of the engine starting time may bereduced, for example. On the other hand, in some circumstances it may bebeneficial to create a vacuum in the cylinder so that fuel can beinjected at the same time as the intake valve is opened during an enginerestart so that fuel may vaporize better. Note that it is also possibleto control selected valves to be held closed between the period betweenthe request to stop and the actual engine stop or between the enginestop and engine start period. That is, valves do not have to be heldclosed during the entire period between the request to stop and asubsequent restart. The valves may be held closed during a fraction ofthe period from the shutdown request to restart depending on objectives.

By closing the intake and/or exhaust valves after a request to stop theengine, and by maintaining the intake valves in a closed position, flowinto the exhaust and out of the engine may be reduced. This can beespecially important when stopping engines that have electricallyactuated intake valves that assume a neutral position while in adeactivated state (e.g., see FIG. 3) since valves in the deactivatedstate may allow flow through the engine and exhaust. In addition, asmentioned above, valves that are opposite the commanded closed valves(e.g., if intake valves are commanded closed the opposite valve is anexhaust valve or if an exhaust valve is commanded closed the oppositevalve is an intake valve) may be commanded to an open or partially openposition. This may reduce power consumption and/or engine pumping lossesas the engine decelerates and when the engine is stopped. Also, afraction of the engine cylinder valves may be controlled in this manner.That is, valves of three cylinders of a six cylinder engine may becontrolled by one or more of the above mentioned methods. FIGS. 6-8illustrate a few of the possible engine shutdown and starting sequencesavailable and as such are not meant to limit the breadth or scope of thedescription. The routine proceeds to step 408.

In step 408, the routine assesses the state of one or more cylinders todetermine if the last combustion cycle has been completed. If the lastcombustion cycle of the cylinders has not completed the routine returnsto step 404. If the last combustion cycle of the cylinders has completedthen the routine proceeds to step 410.

Note: the execution of step 406 may be replaced by step 408 and step 408may be replaced by step 406 if it is desired to complete the lastcylinder combustion event prior to holding selected valves closed.

In step 410, the routine determines if the engine rotation has stopped.If engine rotation has not stopped the routine closes appropriate valvesto reduce flow through the engine and to reduce engine noise by one ofthe above-mention methods, for example, and waits until the enginestops. The routine proceeds to step 412.

In step 412, the engine controller may release selected valves. Somevariable event valvetrains may employ valves that consume power in theopen and/or closed position, the electrically actuated valves describedby FIG. 3 for example. In these systems it may be beneficial to releaseone or more variable event valves so that electrical power consumptionmay be reduced during the engine stop. Intake and/or exhaust valves maybe released if it is determined that flow through the engine cylinderwill be small when the valve is released, if the battery state of chargeis low, or if it is desirable to conserve electrical power, for example.The routine proceeds to step 414.

In step 414, the routine determines if the remaining closed valvesshould be released. The routine can make the determination by evaluatingengine stop time (the amount of time that the engine has been stoppedalso known as the engine soak time), engine operating conditions (e.g.,engine temperature, battery state of charge), operator inputs, inputsfrom ancillary systems (e.g., hybrid powertrain controllers) and/or fromcombinations or subcombinations of the previously mentioned conditions.If none of the previously mentioned inputs indicate that the valvesshould be held in a position then the routine proceeds to step 416. Ifconditions to release the valves are not met the routine proceeds toexit.

In step 416, the remaining valves that are held in a position arereleased. As mentioned previously, some variable event valvetrains mayconsume power when commanded to the closed state, for example.Therefore, it may be beneficial to reduce power consumption by releasingthe valves and/or reducing or stopping power flowing to these valves.Some electrically actuated valves use permanent magnet armatures orpoles that allow the valve to stay in a closed position if the pressuredrop across the valve is below a certain amount. For these types ofvalve actuators it is possible to release the valve and inhibit flowthrough the cylinder by stopping power flowing to the valve since thepermanent magnet provides the force to hold the valve in a closedposition. After releasing the valves the routine proceeds to exit.

Referring to FIG. 5, a flow chart of a method to start an engine withvalves held in a closed position is shown. In step 501, the routinedetermines if there has been a request to start the engine. If so, theroutine proceeds to step 503. If not, the routine proceeds to exit.

In step 503, valves are positioned based on the engine stoppingposition, cylinder firing order, and the engine starting requirements.Since valves may be held in a position during engine shutdown and stopthe position of some valves relative to the desired stroke (e.g.,intake, compression, exhaust, or power stroke) of a specific cylindermay be out of synchronization. For example, based on the position ofpistons it may be desirable to set cylinder number one to an intakestroke. However, the intake valves of cylinder one may be held in theclosed position if the engine is stopped using the method described inFIG. 4. Consequently, in step 503, the engine valves may be commanded toa desired position that is related to the engine position, desiredfiring order, and engine starting requirements. Therefore, in acondition where the intake valves are closed during an engine restartrequest and where an intake event is desired, the valve may be movedfrom a closed position to an open position, for example. One method fordetermining the desired stroke and valve sequence for a variable eventvalvetrain is described in U.S. patent application Ser. No. 10/805,645filed Mar. 19, 2004 which is hereby fully and completely incorporated byreference. The method proceeds to step 505.

In step 505, the engine is started. After the valves are set to desiredpositions the engine may be started by assistance from a starter motor,directly started (started by combusting an air-fuel mixture in one ormore cylinders), or started by a hybrid motor. As the engine rotates thevalves are operated in a predetermined sequence (e.g. four-stroke orsix-stroke) to operate the engine. After starting the routine proceedsto exit.

Note that the methods described by FIGS. 4 and 5 may be used to producethe engine valve sequences illustrated in FIGS. 6-8 and other sequencesnot presently illustrated. As such, FIGS. 6-8 are not meant to limit thescope or breadth of the description but merely as examples forillustration purposes.

Referring now to FIG. 6, an example valve timing sequence during anengine stop and subsequent start is shown. The illustrated sequence is asimulation that represents valve control for a four cylinder engineoperating in a four-stroke cycle. Since it is possible to achieve thevarious illustrated valve trajectories present in the description usinga variety of actuator types (e.g., electrically actuated, hydraulicallyactuated, and mechanically actuated), the type or design of the actuatoremployed is not meant to limit or reduce the scope of the description.In this example, the trajectories represent possible trajectories forelectrically actuated valves.

The intake and exhaust valve position histories go from the left to theright hand side of the figure. The intake valve trajectories are labeled11-14 while exhaust valve trajectories are labeled E1-E4. At thebeginning of each valve trajectory (i.e., the left hand side of thefigure) is displayed the letters O, M, and C. These letters identify thevalve open (O), mid (M), and closed (C) positions. The vertical markersalong the valve trajectories identify the top-dead-center orbottom-dead-center positions for the respective cylinders. Vertical line601 represents an example of an indication of where in time a request tostop the engine has occurred, vertical line 603 indicates the enginestopping position, and vertical line 607 indicates a request to startthe engine. Engine fuel injection timing is indicated by fuel droplets(e.g., 620) and engine spark timing is indicated by an “*”. Fuelinjection timing for a port injected engine is shown. The valve timingand engine position markers can be related to the piston position ofeach cylinder of the engine (e.g., lines 610 and 612). Pistons 1 and 4are in the same positions in their respective cylinders while cylinders2 and 3 are 180° out of phase with cylinders 1 and 4.

After a request to stop 601, the intake valves remain closed until theengine start request. In this example, the stop request occurs during anintake event of cylinder 2 and the injection timing is performed whenthe intake valve of the respective cylinder is closed. The intake valveis shown finishing the induction event that is in progress. However, itis also possible to shut the intake valve earlier after a request tostop so that the cylinder charge is reduced. The last combustion eventprior to engine stop occurs in cylinder 2 since the intake valves of theremaining cylinders are held closed after the stop request. The exhaustvalves continue to operate until the contents of the respectivecylinders are exhausted and then they are held in a closed position.Alternatively, the exhaust valves can be held closed after a request tostop until the engine stops without having exhausted the cylindercontents. That is, the exhaust valves can be held closed after a requestto stop without exhausting the cylinder contents. Further, it is alsopossible to close all cylinder valves while inhibiting combustion (e.g.,by inhibiting the ignition spark) after the request to stop so that anair-fuel mixture is trapped within the cylinder. By trapping an air-fuelmixture in the cylinder it may be possible to reduce starting time bycombusting the mixture during a subsequent engine start request.

Region 605 is between engine stop and engine start. This regionrepresents the engine off or engine soak period and it may vary induration. As such, the soak time is meant for illustration purposes onlyand is not intended to define any specific duration. The engine may berestarted after this period by cranking the engine or by directlystarting the engine by injecting fuel into cylinders holding trappedair, for example. The figure also shows that all engine valves are heldclosed during the soak period. By holding the valves closed engineevaporative emissions and disruption of the catalyst state may bereduced since air flow into the engine may be reduced while enginerotation has stopped. Alternatively, it is also possible to release oneor more of the valves to the valve middle position so that one group ofvalves is held closed while a second group of valves is released to themiddle position. Further, the valves may be released to the middleposition in response to an amount of time since engine stop, an engineoperating condition (e.g., engine temperature, catalyst temperature,condition of a hybrid powertrain, or battery state of charge), or untilan external request such as a request by a hybrid powertrain controller,for example.

The engine is restarted by setting the timing of the valves. The valvesmay be set to the timing that they operated at prior to the engine stoprequest or they may be timed such that the engine initiates a firstcombustion event at a predetermined cylinder, for example. In thestarting event illustrated in FIG. 6 fuel is injected during an openvalve of cylinder 2 and is combusted thereafter. In this example, thestarting request initiates the opening of cylinder 2 intake valve 625and cylinder 1 exhaust valve 630. Operation of the other valves followbased on a four-stroke cycle that is relative to the position of therotating engine.

Referring now to FIG. 7, an alternate example valve timing sequenceduring a stop and subsequent start of a four cylinder engine is shown.The illustrated sequence is similar to that shown in FIG. 6 and uses thesame designations for valves, valve positions, spark, and fuel timing.However, in this sequence fuel directly injected into the cylinder isrepresented.

Vertical line 701 represents an example of an indication of where intime a request to stop the engine has occurred, vertical line 703indicates the engine stopping position, and vertical line 707 indicatesa request to start the engine. Engine fuel injection timing is indicatedby fuel droplets (e.g., 720) and engine spark timing is indicated by an“*”. The valve timing and engine position markers can be related to thepiston position of each cylinder of the engine (e.g., lines 710 and712). Pistons 1 and 4 are in the same positions in their respectivecylinders while cylinders 2 and 3 are 180° out of phase with cylinders 1and 4.

After a request to stop 701, the intake valves remain closed until theengine start request. In this example, the stop request occurs during anintake event of cylinder 2 and causes an early closure of cylinder 2intake valve. Since fuel is directly injected into the cylinder theinjection is may occur while the intake valve is open or while theintake valve is closed. The last combustion event prior to engine stopoccurs in cylinder 2 since the intake valves of the remaining cylindersare held closed after the stop request. The exhaust valves continue tooperate as if the respective cylinders were operating in a four-strokevalve timing mode. Alternatively, the exhaust valves can be held closedafter a request to stop until the engine stops without having exhaustedthe cylinder contents or they may be held closed after the respectivecylinder are exhausted. Further, it is also possible to close allcylinder valves while inhibiting combustion (e.g., by inhibiting thefuel and/or spark delivery) after the request to stop.

Region 705 is between engine stop and engine start. This regionrepresents the engine off or engine soak period and it may vary induration. As such, the soak time is meant for illustration purposes onlyand is not intended to define any specific duration. The engine may berestarted after this period by cranking the engine or by directlystarting the engine by injecting fuel into cylinders holding trappedair, for example. The figure also shows that exhaust valves are releasedafter the engine reaches a stop position. By releasing the exhaust valveit may be possible to reduce power consumption of electrically actuatedvalves while the engine is not operating. Further, since the intakevalves remain closed, engine evaporative emissions and disruption of thecatalyst state may be reduced since air flow into the engine may bereduced while engine rotation has stopped. As mentioned above, thevalves may be released to the middle position in response to an amountof time since engine stop, an engine operating condition (e.g., enginetemperature, barometric pressure, catalyst temperature, condition of ahybrid powertrain, or battery state of charge), or until an externalrequest such as a request by a hybrid powertrain controller, forexample. Further still, one group of valves may be held in the positionthe valve assumed at engine stop while others are positioned and/orreleased in response to operating conditions of the engine and/orvehicle.

After a start request, the engine is restarted by setting the timing ofthe valves. The valves may be set to the timing that they operated atprior to the engine stop request or they may be timed such that theengine initiates a first combustion event in a predetermined cylinder,for example. In the starting event illustrated in FIG. 7 fuel isinjected after a cylinder 2 valve opening and is combusted thereafter.In this example, the starting request initiates the opening of cylinder2 intake valve 725, cylinder 1 exhaust valve 730, and cylinder 4 exhaustvalve 731. By opening cylinder 1 and 4 exhaust valves early it may bepossible to improve the spin up of a turbo charger. Operation of theother valves follow based on a four-stroke cycle that is relative to theposition of the rotating engine crankshaft.

Referring now to FIG. 8, an alternate example valve timing sequenceduring a stop and subsequent start of a four cylinder engine is shown.Again, the illustrated sequence is similar to that shown in FIG. 6 anduses the same designations for valves, valve positions, spark, and fueltiming. However, in this sequence fuel directly injected into thecylinder is represented.

Vertical line 801 represents an example of an indication of where intime a request to stop the engine has occurred, vertical line 803indicates the engine stopping position, and vertical line 807 indicatesa request to start the engine. Engine fuel injection timing is indicatedby fuel droplets (e.g., 820) and engine spark timing is indicated by an“*”. The valve timing and engine position markers can be related to thepiston position of each cylinder of the engine (e.g., lines 810 and812). Pistons 1 and 4 are in the same positions in their respectivecylinders while cylinders 2 and 3 are 180° out of phase with cylinders 1and 4.

After a request to stop 801, the intake valves remain closed until latein the soak period. In this example, the stop request occurs during anintake event of cylinder 2 but the intake valve timing is maintained.Since fuel is directly injected into the cylinder the injection can bemade after the intake valve is closed. The last combustion event priorto engine stop occurs in cylinder 2 since the intake valves of theremaining cylinders are held closed after the stop request. The exhaustvalves continue to operate until exhaust gases are expelled from therespective cylinders and then they are held closed until late in thesoak period. Alternatively, the exhaust valves can be held closed aftera request to stop until the engine stops and then released withouthaving exhausted the cylinder contents during engine rotation or theymay be held closed after the respective cylinder are exhausted duringengine rotation.

Region 805 is between engine stop and engine start. This regionrepresents the engine off or engine soak period and it may vary induration. As such, the soak time is meant for illustration purposes onlyand is not intended to define any specific duration. The engine may berestarted after this period by cranking the engine or by directlystarting the engine by injecting fuel into cylinders holding trappedair, for example. The figure also shows that intake and exhaust valvesare released later in the soak period. By releasing the valves it may bepossible to reduce power consumption while the engine is not operating.As mentioned above, the valves may be released and/or positioned to themiddle position in response to an amount of time since engine stop, anengine operating condition (e.g., engine temperature, catalysttemperature, barometric pressure, or battery state of charge), or untilan external request such as a request by a hybrid powertrain controller,for example. In other words, the valves may be deactivated and/orreleased after a predetermined period that may be influenced by one ormore of the previously mentioned conditions or factors. Thus, the enginevalves may be positioned and/or released to a desired position, inresponse to vehicle/engine operating conditions, after an engine stopand before a request to start the engine. Further, the valves may besplit up into two or more groups that are positioned and/or released atdifferent times during the engine stop. This allows different valvesequences between different starting and stopping conditions so that thedesired control objectives may be achieved.

The engine can be restarted by setting the timing of the valves from themid position and proceeding in a manner similar to that described inFIG. 7. Further, in an alternate embodiment of the starting sequencesshown in FIGS. 6-8, the engine may be directly started (i.e., where fuelcan be directly injected into a cylinder) so that intake and exhaustvalves can be closed or held closed during an engine restart (i.e., thevalves do not have to be commanded to the full open position). Furtherstill, since it is possible to actuate variable event valvetrainsindependent of crankshaft position, it is possible to start pairs ofcylinders that have pistons in the same cylinder position and thentransition the cylinders to a different more conventional firing order.For example, a four cylinder engine may be started by initially firingcylinders 1 and 4 as a pair and cylinders 2 and 3 as a pair. The valvetiming of each cylinder pair may be set so that the cylinders induct andexhaust at the same position relative to the crankshaft. In thisstarting scenario it may be beneficial to exhaust the cylinder contentsof one or more cylinder pairs before combustion in the cylinder pair isinitiated. By exhausting the cylinder pair simultaneously, the speed ofa turbo charger turbine located downstream of the cylinders may beincreased at a higher rate during cylinder reactivation or enginestarting.

Also note that it is possible for some electrically actuated valves toremain in a closed position after the valve is electrically released.That is, power flow to the valve has been stopped. For example,permanent magnet valves can be electrically released (i.e., no longersupplied by current or supplied at a lower level of current, orhydraulic pressure) and maintain a closed position since the attractiveforce of the permanent magnet can hold the actuator armature in a closedposition. Therefore, the valve releases illustrated in FIGS. 6,7, and 8may also be interpreted as electrically or hydraulically releasing thevalve and are therefore not meant to limit the scope or breath of thedescription.

Combinations and sub-combinations of the features illustrated in FIGS.6-8 may be made in an order that may not be illustrated here but iswithin the scope of the description and as such FIGS. 6-8 are notintended to limit the scope or breadth of the description.

Referring now to FIG. 9, a flow chart of a routine to deactivatecylinders of an engine having variably actuated valves and two turbochargers that are coupled to two cylinder banks through individualintake manifolds is shown. The description of FIG. 9 is made inreference to the configuration illustrated in FIG. 2 a but may beapplied to FIG. 2 b as well, particularly if a second throttle or valveis used to isolate the turbo charger compressor outputs. In other words,in another embodiment of the system described in FIG. 2 b is configuredwith a throttle or valve that can block the air flow from the activeturbo charger to the deactivated turbo charger. The valve or throttlecan prevent reversal rotation of the deactivated compressor when theengine goes into a cylinder deactivation mode, for example.

When a turbo charger compressor 237 rotates it draws air from the inletside, compresses the air, and directs the air to the outlet side.Consequently, a negative pressure can develop at the turbo charger inletand a positive pressure can develop at the turbo charger outlet. Theturbo charger compressor can continue to rotate and compress air fromthe inlet side of the turbo charger as long as exhaust energy issupplied to the turbine side of the turbo charger. However, during lowerengine loads it may be desirable to deactivate a group of cylinders(e.g., 210, 212, 214) by closing the intake and/or exhaust valves of thecylinders, for example. Closing the intake and exhaust valves duringcylinder deactivation can trap air and/or exhaust gas in the cylinder sothat cylinder pumping work and oil consumption are reduced. Further,deactivating the cylinder group may improve the operating efficiency ofthe active cylinder group since the remaining cylinders may operate in aregion where thermal efficiency is increased and pumping losses arereduced.

When a cylinder group that supplies exhaust gases to a turbo charger isdeactivated the energy input to the turbo charger is decreased and theturbo charger turbine speed will decrease. If the flow of exhaust energyis stopped long enough, compressor rotation may stop and/or reversedirection. This occurs because when exhaust flow to the turbine isstopped the pressure across the turbine can reach equilibrium so thatthere is little, if any, pressure drop across the turbine. If there isno pressure drop across the turbine then the turbine cannot generatetorque to rotate the turbo charger compressor. On the other hand,deactivating the intake valves of a cylinder stops the flow of airthrough the respective cylinder and can cause the pressure at the outletof the turbine to increase as the inertial energy of the compressorcontinues to cause the compressor to rotate. Further, the inlet side ofthe compressor can also be low due to the pumping operation of thecompressor. Naturally, the higher pressure air on the outlet side of thecompressor seeks a reduced energy state which can be achieved byreversing the rotation of the compressor and flowing air from the outletside of the compressor to the inlet side of the compressor. Reverserotation of the compressor is not prevented by the turbine becauseexhaust pressure equilibrates and reduces the pressure drop across theturbine.

It may be undesirable to reverse rotation of the compressor since it canincrease the amount of time it takes the compressor to reach anefficient operating speed after the cylinder group is reactivated.Furthermore, reverse compressor rotation may make it more difficult toaccurately determine air flow through the engine. The method describedin FIG. 9 can reduce the possibility of compressor reverse rotation andcan further provide a smoother cylinder deactivation transition.

In step 901, the routine determines if cylinder deactivation has beenrequested. If not, the routine exits. If so, the routine proceeds tostep 903.

In step 903, operation of the turbo charger in communication with thegroup of cylinders to be deactivated is adjusted. The turbo chargerefficiency and speed are lowered by adjusting the vane position oropening the waste gate of the turbo charger. This reduces thepossibility of increasing pressure on the outlet side of the turbocharger compressor before the cylinder group is deactivated, therebyreducing the possibility of compressor reverse rotation.

In addition, the routine begins to adjust the torque generated by theactive cylinder group to compensate for the torque loss associated withlowering the turbo charger efficiency of the cylinder group that will bedeactivated. The active cylinder group torque can be increased byadjusting valve timing, moving the throttle position, increasing turbocharger boost, or by combinations of these devices, for example. Onemethod to control engine torque in a coordinated manner is to usemultivariable feedback on cylinder flow, intake manifold pressure, andexhaust manifold pressure. Further, estimates of control actions thatattempt to achieve the desired control can be included. The actuatorscan be coordinated via a minimization of an objective function of theform:

$Q = {{\frac{1}{2}{\gamma_{1}( {W_{cyl} - W_{{cyl},d}} )}^{2}} + {\frac{1}{2}{\gamma_{2}( {p_{i} - p_{i,d}} )}^{2}} + {\frac{1}{2}{\gamma_{3}( {p_{e} - p_{e,d}} )}^{2}}}$

where ( )_(d) denotes the desired set-points for cylinder flow, W_(cyl),intake manifold pressure, p_(i), and exhaust manifold pressure, p_(e)respectively. The parameters γ₁,γ₂,γ₃ represent calibration variableswhich can be used to shape the transient performance. The function Qinstantaneously depends only on the valve timing; hence the valvetiming, IVC, can used to minimize this term. Setting valve timing toreduce Q results in the following equation:

$Q = {\overset{\_}{Q} = {{\frac{1}{2}{\gamma_{1}( {{{\overset{\_}{W}}_{cyl}( {p_{i},p_{e},W_{{cyl},d}} )} - W_{{cyl},d}} )}^{2}} + {\frac{1}{2}{\gamma_{2}( {p_{i} - p_{i,d}} )}^{2}} + {\frac{1}{2}{\gamma_{3}( {p_{e} - p_{e,d}} )}^{2}}}}$

where W _(cyl)(p_(i),p_(e),W_(cyl,d)) denotes the closest achievablecylinder flow to the desired set-point. If the desired set-point isachievable then W _(cyl)(p_(i),p_(e),W_(cyl,d))=W_(cyl,d). The desiredset-point for the cylinder flow may not be achievable during someconditions because of lower or upper valve duration limits. Next, Q canbe reduced using electronic throttle and turbine actuation. Since theinstantaneous value of Q cannot be affected by the electronic throttleand/or turbine actuation the expansion

${\overset{\_}{Q}( {t + {\Delta \; t}} )} = {{\overset{\_}{Q}(t)} + {\Delta \; {t \cdot \frac{\overset{\_}{Q}}{t}}}}$

is considered and a controller is derived to reduce a weighted sum of

$\frac{\overset{\_}{Q}}{t},$

control effort, and the increment of control effort involved. It followsthen that the desired throttle flow has the form:

$W_{{th},c} = {W_{{th},d} + {K_{1}\frac{\partial\overset{\_}{Q}}{\partial p_{i}}} + {K_{2}{\int_{0}^{t}{\frac{\partial\overset{\_}{Q}}{\partial p_{i}}{t}}}}}$

while the desired turbine flow has the form:

$W_{{tu},c} = {W_{{th},d} + {K_{3}\frac{\partial\overset{\_}{Q}}{\partial p_{e}}} + {K_{4}{\int_{0}^{t}{\frac{\partial\overset{\_}{Q}}{\partial p_{e}}{t}}}}}$

The throttle position and turbine position can then be determined sothat they produce the desired flow rates by inverting the respectivethrottle and turbine flow characteristics. The coordinated control ofthrottle, valves, and turbo charger described above may be used tocontrol cylinder flow for dual or single intake manifolds similar tothose described in FIGS. 2 a and 2 b. The routine proceeds to step 905.

In step 905, the routine commands a vacuum or negative pressure in theintake manifold 222. By creating a pressure depression in the intakemanifold it is possible that any residual positive pressure between theturbo charger compressor and throttle causes flow toward the intakemanifold and thus reduces the possibility of reversing the rotation ofthe compressor.

A vacuum is created in intake manifold 222 by closing throttle 252 andif desired the valve timing of cylinder intake valves. The desiredintake manifold vacuum may be determined from engine and/or turbocharger operating conditions prior to the cylinder deactivation request.For example, if the engine were operating at a higher speed and with ahigher flow rate through the compressor, then a lower intake manifoldpressure would be commanded so that there is a better possibility ofstopping compressor rotation reversal. If the engine were operating at alower speed and lower air flow rate, idle for example, a higher manifoldpressure could be commanded since there would be less air pressure todissipate between the turbo charger compressor and the throttle body.The routine continues to step 907.

In step 907, a cylinder group is deactivated and torque is compensatedin the active cylinder group. The cylinder group is deactivated in orderof combustion (e.g., for an eight cylinder having a firing order of1-5-4-2-6-3-7-8 cylinders could be deactivated in 5-2-3-8 order) so thatcylinders can complete a combustion event before being deactivated.During the deactivation period the intake and exhaust valves are held ina closed position to prevent flow through the cylinder. The exhaust fromcombustion may be trapped in the cylinder or it may be exhausted to theexhaust manifold. For port injected engines, trapping exhaust incylinder allows the cylinder to act as an air spring and reduces thepossibility of drawing oil into the cylinder since a positive pressurecan be maintained in the cylinder for a large portion of the cylindercycle. However, for an engine having fuel directly injected into thecylinder, air could be trapped in the cylinder during cylinderdeactivation so that cylinder could be reactivated quicker since exhaustwould not have to be expelled in to the exhaust manifold before thecylinder is restarted.

In addition, the output torque of cylinders in the active cylinder groupis increased to compensate for the torque lost by deactivatingcylinders. As mentioned above, a cylinder torque increase may beachieved by adjusting valve timing, increasing boost, controlling thethrottle, or by spark timing, for example. In one example, therespective valve timings can be determined by the method illustrated inU.S. patent application Ser. No. 10/805,642 filed Mar. 19, 2004 which ishereby fully incorporated by reference. The routine exits afterdeactivating the desired cylinder group and compensating for the relatedtorque loss.

Referring now to FIG. 10, a flow chart for a cylinder reactivationmethod is shown. In step 1001, the routine determines if a request toreactivate cylinders has been made (i.e., to begin combustion innon-combusting cylinders). The request to reactivate cylinders can bebased on one or more vehicle operating conditions. For example, theengine controller can request activation of cylinders based on operatortorque demand, temperature of an exhaust gas after treatment device,cylinder reactivation after deceleration fuel shut off, engine coolanttemperature, or various combinations of vehicle operating conditions. Ifthere is a request to reactivate cylinders the routine proceeds to step1003, if not, the routine proceeds to exit.

In step 1003, the turbo charger coupled to the deactivated cylindergroup is adjusted. Before exhaust gases are introduced to the turbocharger the vanes of a variable geometry turbo charger or the waste gateof a turbo charger are adjusted so that they bypass little of theexhaust energy at the turbo charger. This can increase the speed andefficiency of the turbo charger. Alternatively, the turbo charger vanesor waste gate can be positioned for restarting the cylinder group anytime between the time that the turbine speed is below a predeterminedlevel and the time when cylinder reactivation is requested. Bypositioning the turbo charger vanes or waste gate to a closed positionbefore exhaust gas is fed to the turbo charger allows more exhaustenergy to be used to accelerate the turbo charger turbine as thecylinders are restarted. However, in some circumstance where the vanesof a turbo charge can be positioned quickly, the vanes can be set to anopen position for a brief period of time or a predetermined number ofcylinder combustion events and then closed. This can improve turbocharge spool-up (i.e., time to reach a desired turbo speed) because flowthrough the turbine is increased and by improving the volumetricefficiency of the engine. Later, when the vanes are closed, additionalexhaust mass is used to increase the boost pressure. The routine thenproceeds to step 1005.

In step 1005, cylinder contents of deactivated cylinders are exhausted.As mentioned above, for port fueled cylinders it may be beneficial totrap exhaust within a cylinder to reduce oil consumption and to reducecylinder pumping losses. However, if the deactivated cylinders containexhaust gas then the contents of each cylinder are exhausted in step1005 by opening the exhaust valves during the exhaust stroke of therespective cylinder. This can reduce the possibility of misfire whenfresh charge is inducted into the cylinder because the dilution of thecharge may be limited. Furthermore, expelling exhaust from the cylindercan cause the turbo charger to begin to spin earlier so that turbo lagis reduced when the cylinders are restarted. Alternatively, for engineshaving fuel injected directly into the cylinder, air can be trapped inthe cylinder during cylinder deactivation so that there is no need toexhaust the cylinder contents prior to initiating combustion in thecylinder. The routine proceeds to step 1007.

In step 1007, the valves of deactivated cylinders are restarted.Cylinders are restarted by opening intake valves of the first availablecylinder to be capable of inducting an air charge and then starting theremainder of cylinders in order of combustion. During the transitionfrom a deactivated cylinder to an active cylinder, a torque disturbancemay be created by reactivating a cylinder or by an error between thedesired engine torque and the torque generated during cylinderreactivation. The engine torque may be smoothed by initially startingthe cylinders with a small charge and then migrating to a larger chargeover a predetermined number of engine combustion events. For example, ifa driver torque demand is to be shared equally between cylinders, and acylinder is transitioning from inactive to active, the cylinder may beinitially reactivated by inducting twenty five percent of the cylindercharge necessary to meet the desired cylinder torque. Then, over anumber of cylinder events the cylinder charge can be increased so thatthe cylinder torque output matches the fraction of desired torque thatthe cylinder is scheduled to contribute. Alternatively, the cylinder maybe reactivated by inducting a charge that matches the desired charge forthe respective cylinder so that the cylinder reactivation occurs over asingle cylinder cycle.

As mentioned above, cylinder reactivation can be initiated by driverdemand or by other means. If the engine torque command is increasing ata sufficiently high rate it may be difficult for the engine torque tofollow the desired torque because the turbo charger speed and efficiencymay be low. Consequently, if the cylinder air flow rate is increasedbeyond an air flow rate that the turbo charger compressor can supply atthe current operating conditions, then the cylinder torque may betemporarily reduced. This condition may be prevented by adjusting anactuator to vary the cylinder air charge as the air flow rate of theturbo charger varies. By limiting the valve timing, the cylinder aircharge may be controlled such that the cylinder air charge increasesmonotonically as the desired torque moves from a lower value to a highervalue. In one example, the intake valve closing position may beconstrained by the following equation:

W _(c) ≧W _(cyl)(p,IVC,n,bp)

Where W_(c) is the turbo charger compressor mass flow, W_(cyl) is thecylinder mass flow rate as a function of intake manifold pressure (p),intake valve closing location (IVC), engine speed (n), and barometricpressure (bp).

During some engine operating conditions (e.g., where there isdegradation of a valve or valve controller) it may be beneficial tooperate a variable event valvetrain at a fixed valve timing (i.e.,operating at least a valve of a cylinder at a fixed open and closedduration relative to crankshaft position). The cylinder air amount maybe adjusted by controlling the flow rate of a turbo charger and theposition of a throttle where both devices are located upstream of thefixed timing valve. In addition, it is possible to have different valvetiming modes (e.g., fixed and variable) that are selected in response toengine operating conditions (e.g., engine temperature, time since enginestart, or degraded performance of a valve controller). Where valvetiming is fixed, cylinder air charge can be adjusted, as mentionedabove, by controlling the turbo charger compressor flow rate and by thethrottle position. On the other hand, where valve timing is variable,cylinder air charge may be adjusted by adjusting the turbo chargercompressor flow rate, valve timing, and the position of the throttleplate. The routine continues to step 1009.

In an alternative embodiment cylinder flow may be based on theexpression:

W _(cyl,d)(k+1)= W _(cyl,d)(k)(1−κ(t))+W _(cyl,d)(k)κ(t)

Where 0<κ(t)<1 is maximized subject to the constrain that the estimatedcylinder flow is monotonic.

In step 1009, the output torque of cylinders in the active cylindergroup is adjusted based on the torque produced by the reactivatedcylinders and by the desired engine torque.

Prior to cylinder reactivation, the charge amount (air and fuel) of theactive cylinders is at a higher level than if all cylinders were activeso that equivalent torque may be produced by fewer cylinders. This canincrease the thermal efficiency and reduce the pumping losses of thecylinders because the pressure in the intake manifold is increased tomeet the desired cylinder charge amount. During the cylinderreactivation transition, the charge in the active cylinders is reducedby adjusting valve timing of active cylinders so that the additionaltorque provided by cylinders that are being reactivated is compensated.In other words, the desired engine torque is produced by increasing thecylinder air charge of some cylinders and decreasing the cylinder aircharge of other cylinders. This can be achieved by changing the valveopening duration, changing the valve closing position with respect tothe crankshaft, or by changing the valve lift. Further, the enginetorque may be reduced by retarding spark or by retarding spark andadjusting valve timing of the active cylinders. In this way, the enginetorque output may be smoothed so that noticeable changes in engineoperation are reduced. In addition, other torque disturbance rejectiontechniques may also be applied. For example, the clutches in atransmission coupled to the engine can be allowed to slip, or the torqueconverter clutch pressure can be reduced. The routine proceeds to step1011.

In step 1011, manifold pressures are balanced between the two cylinderbanks. The desired engine torque is produced by providing substantiallyequivalent torque (e.g., ±20 N-M) from both cylinder banks. This may beaccomplished by controlling the intake manifolds to the same pressureand by operating the valve timings between the banks in a substantiallysimilar manner (e.g., opening and closing times of the valves within ±15Crankshaft angle degrees). Further, the throttles and turbo chargers canbe operated in a substantially similar manner. However, if there is anoticeable difference between the cylinder group/bank air-fuel ratios orin the amount of fuel delivered to each cylinder group/bank to produce adesired air-fuel ratio, for example, then the throttles, valves, andturbo chargers can be adjusted by feedback control so that the cylinderbank outputs are more closely matched.

Controller 12 determines a desired pressure for the intake manifold 44.The desired pressure is based on canister vapor purge pressure, enginenoise and vibration, and brake boost requirements. If the desiredmanifold pressure is below atmospheric pressure then the variablegeometry turbo charger can be set to an open position and the throttlefeedback controlled to set the desired manifold pressure. The valvetimings are based on the desired manifold pressure and desired enginetorque. On the other hand, if the desired manifold pressure is aboveatmospheric, then the throttle can be held open and then the cylinderair charge can be regulated by position of the VGT vanes and the valvetimings. A similar strategy can be implemented by adjusting the wastegate position of a waste gate turbo charger as well.

Each of the intake manifolds are commanded to substantially equalpressures (e.g., ±0.07 bar) so that engine torque can be balancedbetween the cylinder groups. Furthermore, the cylinder groups can beoperated at substantially similar valve timings. However, it is alsopossible to operate a first manifold that is in communication with afirst cylinder group at a first manifold pressure while operating asecond intake manifold at a second pressure so that one manifold may beused to supply vacuum to ancillary devices (e.g., brake boost andcrankcase ventilation). Valve timing and/or lift may be adjusted betweenthe cylinder groups so that each cylinder group provides substantiallythe same engine torque even though the manifold pressures may bedifferent. For example, an engine with two intake manifolds can beoperated so that pressure in one manifold is near atmospheric pressure(±0.07 bar) while the other manifold is operated 0.24 bar belowatmospheric pressure. Coordination between valves, throttle, and turbocharger can be accomplished as described in FIG. 9, step 903.

Referring now to FIG. 11, a flow chart of a routine to deactivatecylinders of an engine with a common intake manifold is shown. In step1101, the routine determines if there has been a request to deactivatecylinders. If so, the routine proceeds to step 1102, if not, the routineexits.

In step 1103, adjustments are made to the operation of the turbo chargerthat is in communication with the group of cylinders that are to bedeactivated. Specifically, the waste gate or vanes are opened so thatthe turbo charger efficiency is reduced and so that the compressor speedis reduced.

In addition, the routine begins to adjust the torque generated by theactive cylinder group to compensate for the torque loss associated withlowering the turbo charger efficiency of the cylinder group that will bedeactivated. The active cylinder group torque can be increased byadjusting valve timing, moving the throttle position, increasing turbocharger boost, or by combinations of these devices, for example.Specifically, in one example, the valve opening duration of activecylinders can be increased so that cylinders of the active group produceadditional torque and when matched with an adjusted fuel amount producea stoichiometric mixture for combustion. In another example, the phaseof the intake valve can be adjusted relative to a crankshaft position sothat the intake valve closing occurs later in the intake stroke of therespective cylinder. The routine proceeds to step 1105.

In step 1105, cylinders of a selected cylinder group are deactivated.The cylinder group is deactivated in order of combustion (e.g., for aneight cylinder having a firing order of 1-5-4-2-6-3-7-8 cylinders couldbe deactivated in 5-2-3-8 order) so that cylinders can complete acombustion event before being deactivated. During the deactivationperiod the intake and exhaust valves can be held in a closed position toprevent flow through the cylinder. The exhaust from combustion may betrapped in the cylinder or it may be exhausted to the exhaust manifold.Port and directly fueled cylinders may be configured as mentioned aboveto trap or expel exhaust gases as desired. The routine proceeds to step1107.

In step 1107, the efficiency of the turbo charger driven by the activecylinder group is adjusted. If the waste gate is partially open or ifthe vanes of a variable geometry turbo charger are at least partiallyopen, then the waste gate or vane position may be reduced so that theturbo charge efficiency increases. As a consequence, the compressor cankeep the intake manifold pressure substantially constant even though theoutput of the other compressor is reduced in step 1103. On the otherhand, if there is little or no room for adjustment, the valve timing andthrottle may be adjusted in step 1109 so that the engine torque may besubstantially maintained through the cylinder deactivation sequence. Theroutine proceeds to step 1109.

In step 1109, the throttle and/or valves of the active cylinder groupare adjusted. Engine torque may be maintained during the cylinderdeactivation process by increasing the cylinder charge of the activecylinders. This can be accomplished by opening the throttle and/or bychanging the valve timing, for example. By controlling the valve timing(e.g., lift, duration, and opening relative to the crank shaft position)charge entering the cylinder can be adjusted to compensate for torqueloss of the deactivated cylinders. The respective valve timings,throttle position, and turbo charger vane position may be determined bythe method mentioned above. The routine exits.

Referring now to FIG. 12, a flow chart of a method to reactivatecylinders is shown. In step 1201, the routine determines if a request toreactivate cylinders has been made (i.e., to begin combustion innon-combusting cylinders). Similar to the method of FIG. 10, the requestto reactivate cylinders can be based on one or more vehicle operatingconditions. If there is a request to reactivate cylinders the routineproceeds to step 1203, if not, the routine proceeds to exit.

In step 1203, the turbo charger coupled to the deactivated cylindergroup is adjusted. Specifically, the turbo charger may be adjusted asdescribed in step 1003 of FIG. 10. The routine then proceeds to step1205.

In step 1205, cylinder contents of deactivated cylinders are exhausted.This step uses the same procedure to expel exhaust gas from a cylinderas that described in step 1005 of FIG. 10. The routine proceeds to step1207.

In step 1207, the valves of deactivated cylinders are restarted.Cylinders are restarted in order of combustion by opening intake valvesand inducting fresh charge. Thereafter the cylinders follow aconventional four stroke cycle. The routine continues to step 1209.

In step 1209, the output torque of cylinders in the active cylindergroup is adjusted based on the torque produced by the reactivatedcylinders and by the desired engine torque.

During the cylinder reactivation transition, the charge in the activecylinders is reduced by adjusting valve timing of active cylinders sothat the additional torque provided by cylinders that are beingreactivated is compensated. In other words, the desired engine torque isproduced by increasing the cylinder air charge of some cylinders anddecreasing the cylinder air charge of other cylinders. Further, theengine torque may be reduced by retarding spark or by retarding sparkand adjusting valve timing of the active cylinders. The routine proceedsto step 1211.

In step 1211, turbo charger turbine speeds are matched between thecylinder groups. Since the output of each turbo chargers is fed to asingle common plenum the cylinders of the two or more cylinder groupswill be exposed to the same inlet pressure plus or minus any differencecaused by the intake manifold runners. Therefore, instead of balancingpressure between separate manifold as is described by step 1011 of FIG.10, turbine speeds are matched between the cylinder groups. This can beaccomplished by commanding the turbine waste gate or variable geometryturbo charger to the same position and then by adjusting the valvetiming of one or both of the cylinder groups. The cylinder air flow ofindividual cylinders can be determined by detecting the oxygenconcentration of the respective cylinder exhaust gas and the amount offuel injected to the cylinder. If the exhaust gas is leaner thanexpected or if the amount of fuel delivered to one cylinder group/bankis greater than the amount delivered to the other cylinder bank then thevalve duration of one cylinder group/bank may be reduced, for example.On the other hand, if the exhaust mixture is richer than expected or ifthe amount of fuel delivered to one cylinder group/bank is less than theamount delivered to the other cylinder bank then the valve duration maybe increased. By adjusting the valve timing the flow of each cylindercan be controlled so that substantially the same amount of air flowsthrough each cylinder. Since the flow of each cylinder is equalized theflow to the turbine is equalized and the turbines can converge tosubstantially the same speed.

Note that when a fuel control system is operating in a closed loop modethe actual cylinder air-fuel mixture will approach the desired air-fuelmixture. In this mode one or more fuel control correction parameters canbe used to compensate the base fuel delivery calculations so that thedesired air-fuel ratio is delivered to a cylinder. That is, the fuelcontrol correction parameter can be multiplied by or added to the basefuel delivery command so that the desired cylinder air-fuel may beachieved. By monitoring the magnitude and sign of the fuel controlcorrection parameter a judgment of the turbo charger output may be made.For example, if the backpressure of one turbo charged cylinder bank ishigher than the backpressure of another cylinder bank, due todegradation of waste gate or vane control for example, then the exhaustof the cylinder bank having a higher backpressure will provide a richermixture that is observable by an exhaust gas oxygen sensor. Theclosed-loop fuel controller in this example would sense that less fuelis required to produce a desired air-fuel mixture, thereby indicating adifference in the cylinder air charge of one of the cylinderbanks/groups. On the other hand, where variations of part tolerancesresult in changes in cylinder air flow, it is possible that the cylinderwith the higher average fuel flow would have a greater fuel flow andtherefore a higher backpressure. In either example, the backpressurebetween the cylinder banks, and therefore the turbine speeds, may bebalanced by adjusting valve timing and/or waste gate/vane position sothat turbo charger operation and the flow through the cylinders may besubstantially equalized (e.g., ±10%), at least under some conditions.

Variation of waste gate or vane geometry of each turbo charger can becompensated by fixing the command of the first turbo charger, fixing thevalve timing, and fixing the throttle position, and then varying thecommand to the second turbo charger. This will allow the second turbocharger efficiency to be raised or lowered so that the manifold pressurewill be changed. Then, the second turbo charger command can be fixed ata command as the command to the first turbo charger is varied. In thisway, the influence of each turbo charger command can be related to thechange in intake manifold pressure and/or cylinder air-fuel ratio sothat the output of each turbo charger can be trimmed to a desired levelbased on the respective change in manifold pressure and/or cylinderair-fuel ratio. Further, the turbo charger adjustment and the resultingair flow change can be used to adapt turbo charger control parameters orto provide on-line way of determining turbo charger degradation. Thisprocedure is not limited to cylinder reactivation, but may be appliedwhenever balancing the turbo charger flow between cylinders is desired.

Also note that the methods described by FIGS. 9-11 can be used tocontrol an engine as illustrated by FIGS. 13 and 14. Of course,variation of the signals illustrated in FIGS. 13 and 14 is possiblewithout departing from the scope or breadth of the present description.Further, the methods described above may be used on single turbo chargerconfigurations. For single turbo charger configurations the controlsoperating on the second turbo charger are eliminated, however, theactive turbo charger flow and active group of valves are controlled incoordination with the deactivating group of cylinders.

Referring now to FIG. 13, a plot of selected example signals of interestfor a simulated cylinder deactivation sequence is shown. Vertical line1301 represents a request to deactivate cylinders. The cylinderdeactivation request may be based on driver demand or it may be based ona request from an ancillary control module, a hybrid valve controlmodule for example.

The sequence labeled “PIP” shows engine position of a four cylinderengine and the top-dead-center location of each cylinder is representedby the rising edge located to the left of the respective cylindernumber. The turbine speed of the cylinder group to be deactivated,Turbine 1 Speed, begins to be reduced to the left of line 1301. Thespeed reduction is the result of opening the turbine vanes or a wastegate. The electrically controlled throttle 125 also begins to close tothe left of line 1301 so that vacuum is reduced in the intake manifold.This tends to keep the compressor spinning in a forward flowingdirection so that air flows toward the cylinders even after the intakevalves are deactivated. On the other hand, if the intake valves wereheld closed while the compressor continued to spin and while the intakemanifold pressure were above atmospheric pressure, it is possible thatthe manifold pressure would cause the compressor direction to reversesince energy flow from the deactivated cylinders would be reduced.

The active cylinder counter, labeled “Cylinder Counter”, shows thelocation where the cylinders are deactivated (1302, 1303). Two of thecylinders, cylinders 2 and 3 for example, are deactivated after theintake manifold pressure reaches a predetermined level. This level mayvary with engine operating conditions and barometric pressure, forexample. The cylinders can be deactivated by stopping fuel flow to thecylinder group and/or by holding one or more of the cylinder valves in aclosed position. The cylinders are deactivated in order of combustion.For example, for a four cylinder engine with a firing order of 1-3-4-2cylinders 2 and 3 can be deactivated by deactivating cylinder 3, thencylinder 2, or by deactivating cylinder 2, then cylinder 3, depending onwhen the deactivation request occurs. In one embodiment, the intakevalves and exhaust valves are held closed after the deactivation requestsuch that an air-fuel mixture is combusted and trapped in the cylinderuntil the cylinder is reactivated. In another embodiment, at least oneof the intake valves are held closed after the cylinder deactivationrequest and at least one of the exhaust valves are allowed to continueto operate. This allows a combusted air-fuel mixture to be exhaustedwhile reducing or stopping flow through the cylinder.

The speed of the turbine, labeled “Turbine 2 Speed”, driving thecompressor that is in communication with the active cylinders, Turbine 2Speed, is increased after the request to deactivate cylinders. Thisallows the active cylinders can generate power at or near astoichiometric air-fuel ratio to compensate for the deactivatedcylinders. Furthermore, the valve timings, valve lift, and valve phaserelative to the crankshaft of the active cylinder group may be adjustedto compensate for the deactivated cylinders as well. In this way,cylinders of a twin turbo charged engine can be deactivated so thattorque disturbances are mitigated.

Referring now to FIG. 14, a plot of example signals of interest for asimulated cylinder reactivation sequence is shown. Similar to FIG. 13,the sequence labeled “PIP” shows engine position of a four cylinderengine.

The turbine speed of the turbo charger in communication with thedeactivated cylinder group, Turbine 1 Speed, is at a low speed until thecylinder reactivation process starts. Then, as the deactivated cylindersbegin to combust the speed of the turbine increases until a desiredspeed is reached. The desired speed may be inferred by determining thepressure drop across the exhaust turbine or by flow into the intakemanifold, for example. The turbine vanes are closed prior to cylinderreactivation so that a greater percentage of the exhaust energy is usedto accelerate the turbine. Alternatively, the turbo charger vanes may beopen initially and then closed after a predetermined number of cylindercombustion events occur so that the speed of the turbine increases at ahigher rate.

The throttle position, labeled “Throttle”, is also increased after arequest to reactivate cylinders so that engine pumping losses will below when the cylinder reactivation occurs. Alternatively, the throttleplate may be set to a desired position during or after the deactivationprocess so that throttle pre-positioning during cylinder reactivationmay not be necessary. Torque control of the reactivated cylinders may beaccomplished by adjusting valve timing, lift, and/or valve openingphasing with respect to the crankshaft. The valve timing adjustments canbe made on an individual cylinder basis so that the air charge ofreactivated cylinders is varied between cylinders and/or between eventsof an individual cylinder. Thus, the respective cylinder air charges canbe regulated by adjusting throttle position and valve timing.Alternatively, the throttle may be moved before or after the deactivatedcylinders are reactivated so that cylinder air charge is affected mostlyby valve timing during the reactivation process.

The intake manifold pressure can remain near atmospheric pressure or maybe depressed as illustrated by line 1405. Setting the intake manifoldpressure near atmospheric pressure can reduce engine pumping work, butclosing the throttle and lowering the intake manifold pressure canprovide vacuum for brakes, for example, and/or reduce the amount ofinduction noise emanating from the engine system. If the throttle is setpartially open and the valve timing is sufficiently long thenreactivating the cylinder can reduce the intake manifold pressure andthe valve timing may have to be adjusted as the manifold pressure variesto mitigate an engine torque disturbance.

The cylinder counter trace, labeled “Cylinder Counter”, shows the numberof active cylinders and where deactivated cylinders are reactivated. Inthis example, cylinders 2 and 3 are reactivated as the throttle ismoving and as the active cylinder group turbine speed is being reduced.However, it is also possible to hold the turbine speed of the turbocharger that is in communication with the active cylinder group at asubstantially constant speed until the cylinders are reactivated. Inthis example, the engine torque in activated cylinders can be adjustedby changing the valve timing, lift, and/or phase relative to thecrankshaft position so that cylinder reactivation torque disturbancesmay be mitigated.

The turbine speed of the active cylinder group is shown being reduced sothat the engine torque of the active cylinders may be reduced inaccordance with the torque being added to the engine by reactivatedcylinders. The turbine speed can be reduced by changing the vaneposition or by opening the waste gate so that the efficiency of theturbine decreases. By lowering the turbine speed of the turbo chargerthat is in communication with active cylinders the torque of activecylinders may be reduced with less adjustment to the valve actuators.Alternatively, as mentioned above, the turbine speed can be heldsubstantially constant during cylinder reactivation and then it may bereduced thereafter, see line 1407 for example. This may make it easierto control engine torque during cylinder reactivation, at least duringsome conditions.

Referring now to FIG. 15, a flow chart of a method to control valveswhen an engine is stopped is shown. As described above, some variablyactuated valves may be operated with little regard to the position of anengine crankshaft, especially when the engine is stopped. However, somevalves require power to remain in an open or closed position sincesprings used in this type of actuator tend to suspend the cylinder valvein a neutral open position. Consequently, this valve type may be left inthe neutral position when the engine is stopped so that electrical powerconsumption may be lowered. When an operator requests engine operation,the valve position may be altered so that the engine can breathe and bestarted in accordance with a standard four stroke cycle, for example.However, it is also possible that an operator simply intends to operateengine accessories (e.g., a radio or entertainment center) withoutoperating the engine. Further, some people tend to cycle from engine“off” to “accessory on” a number of times with no present desire tostart the engine. The flow chart illustrated in FIG. 15 describes amethod to mitigate the affect of this type of operator behavior whileFIG. 16 illustrates an example valve sequence produced by the method ofFIG. 15 during these conditions.

In step 1501, the engine or valve controller determines the operator'sdesire to start the engine by interrogating the status of an ignitionkey switch or from another switch that may be read such as a door openswitch or a door lock switch, for example. If the key/switch/input is inthe off position the routine exits. If the key/switch/input is in the on(i.e., accessory) or in the start position then the routine proceeds tostep 1503.

In step 1503, the valves are pre-positioned in anticipation of a startrequest. This is the “ready-to-start” state of the engine. The valvesmay be positioned based on a four stroke engine cycle and the presentengine position or they may be positioned so that the engine can startin another manner, 2-stroke direct start (i.e., starter-less) forexample. Each valve may be positioned at a predetermined timeindependent of other valves or groups of valves (i.e., greater than onevalve) may be positioned at times independent of other valve groups. Theroutine proceeds to step 1505.

In step 1505, the engine controller determines if there is a request tostart the engine. If so, the routine proceeds to 1507, otherwise theroutine moves to step 1509. Thus, after the valves are pre-positionedthe engine may be started or the valves may be moved to anotherposition, depending on operating conditions.

In step 1509, a timer is started. The timer is used to determine howlong the valves are to be powered. The timer can be set to expire at apredetermined time that can vary with vehicle operating conditions(e.g., state of battery charge, the amount of battery power beingconsumed, ambient air temp, engine temp, the amount of current beingdrawn by a valve actuator). Further, the timer can be reset each timethe operator toggles the key/switch/input from an off to on position. Inan alternate embodiment, the timer can continue to run until the timeexpires, even if the operator toggles the key a number of times, suchthat the timer expires whether the key has been toggled or not. If thetimer has expired and the key is toggled from “stop” to “accessories”,or from “accessories” to “stop’ after the timer has expired. Then thevalves can then again be pre-positioned to the engine start position.The routine proceeds to step 1511 after the timer has been started.

In step 1511, the routine checks to see if the timer of step 1509 hasexceeded a predetermined duration. The duration may change withoperating conditions such as the temperature of the engine, ambient airtemperature, battery state of charge, or time since the last enginestart, for example. If the time has not expired the routine proceeds tostep 1505, otherwise the routine proceeds to step 1515.

In step 1515, a group of valves are set to a desired state. In oneexample, the valves may be released from an open or closed position sothat they are positioned in the neutral state. In another embodiment,permanent magnets may be used so that the valves may be held in an openor closed position while they are not powered. The routine proceeds tostep 1519.

In step 1519, a second group of valves are set to a desired state. Thevalves may be positioned as described in step 1515. In addition, it ispossible to delay the interval between when group one valves are set andwhen group two valves are set. In this way, the noise and power requiredto set the valves and may be reduced.

Note that FIG. 15, steps 1515 and 1519, describe only two valve groups,but more or fewer valve groups may be set to a desired state withoutdeviating from the scope or intent of the description. In addition, ifthe operator requests a start after the valves are released, but withoutrepositioning the valves from the release position, then the valves arepositioned and the engine is started.

Steps 1521-1525 operate similar to those of steps 1511-1519, but theycover a condition where the driver has keyed “off” after an “accessoryon” condition. Further, it is possible that the driver makes a number ofkey/switch/input transitions before deciding not to start the car. Ifthis were to occur, steps 1521-1525 permit the valves to reach a desiredstate, such as mid position.

In step 1507, the pre-positioned valves are operated in accordance withengine position so that the engine can be started. In other words, ifthe engine is cranked during a start the valves will move based on afour stroke cycle, for example. In an alternative embodiment, thepre-positioned valves may allow the engine to be started without astarter (i.e., directly started) using injected fuel and trappedcylinder air. However, if the timer from step 1509 has exceeded apredetermined value, causing valves to be released, and if there is asubsequent request to start, then the valves are repositioned so thatthe engine is prepared to start. The routine exits if the engine isstarted.

Referring now to FIG. 16, an example plot of valve positions for avehicle that transitions between “off” or “stop mode” and “accessory”mode is shown. The illustrated sequence is similar to those shown inFIGS. 6-8 and uses the same designations for valves and valve positions,but in this sequence the engine position does not change and therequested engine mode is identified by the mode request (Mode Req)trace. The mode request trace is comprised of three states; Run (R),Accessories (A), and Stop (S) which are explained below.

A vehicle can have several control states. The first control state isengine stop where the engine is not operating and where vehicle andengine systems are set to states where power consumption (i.e.,primarily battery power consumption) is low because the vehicle may notbe operated for some time, two weeks for example. When an operator putsthe engine/vehicle into the stop state it is unknown whether thevehicle/engine will remain in this state for a minute or a month.Consequently, the vehicle/engine system is often set to a low energyconsumption state in this mode.

Another possible control state is the “accessory” mode where vehiclesystems are brought to a ready-to-operate or to operating conditions,but where the engine is not operated. In some vehicles this isaccomplished by the driver turning an ignition key to a position thatlies between the start and stop position, for example. However, thisstate or a similar state may be entered by other means, by signals inputfrom a hybrid powertrain controller for example. This state is often aprecursor to starting the engine and therefore can be useful to set thestate of engine valves so that the engine is prepared to start. However,in some circumstances it is possible that the driver or requester doesnot actually request that the engine start, if he/she simply wishes tooperate a radio for example.

Of course, there is also the operating mode where the engine may bestarted and operated. In this mode the operating engine can be used topropel the vehicle and to supply power to ancillary systems (e.g.,radio, intake/exhaust valve controller, lights, etc.) so that thebattery power is not consumed, or alternatively power may be supplied toancillary systems by the battery and by the engine, for example. Thismode may be identified by an operating engine while the ignition key isin the “on” or “accessory” position, for example.

It may be useful during transitions between “engine stop mode”,“accessory mode”, and “engine run mode” to have a method that controlsthe valves in a way that improves engine starting while reducing powerconsumption and/or engine emissions.

At vertical marker 1601 a switch or input instructs the enginecontroller that the driver or an alternate source has requested thatengine/vehicle accessories be enabled. The change in requested state isidentified by the change in signal level of the Mode Req signal. Thisexample illustrates an electrically actuated valve being moved from aneutral state to open or closed positions that depend on a desiredstarting sequence, for example. Specifically, the intake valve forcylinder one of a four cylinder engine is set to an open position inanticipation of an intake event of cylinder one. The remaining cylinderintake valves are shown being moved to closed positions at times thatvary so that the valve controller current demand may be reduced and sothat valve noise may be reduced. The exhaust valve for cylinder four isset to an open state so that cylinders one through four are nowconfigured to allow starting the engine in four stroke mode.

At vertical marker 1603 the mode request signal transitions from the“accessory” state to the “stop” state. The distance between marker 1601and marker 1603 (T1) is not intended to imply any specific time durationand as such is not intended to limit the breadth or scope of thedescription. Rather, the time T1 in this illustration is used to show atime interval that has not exceeded the time expired interval of step1511 from FIG. 15. Accordingly, the states of the valves are not changedafter they are initially set from the accessory request at 1601.

Vertical marker 1605 is used to identify another change in the moderequest signal. This time the signal is returned back to the “accessory”position. During the T3 interval valves are released frompre-positioning locations to the neutral state while power flow is cutto others that remain in the open or closed position thanks to forceprovided by permanent magnets acting on the valve armatures. The T3interval illustrates some potential valve state changes that may resultfrom the expiration of the timer in step 1511. Alternatively, the valvesmay be moved to the neutral position in response to an operatingcondition of the engine, a temperature of the engine coolant or of thecatalyst for example.

Vertical marker 1607 shows the last mode request change of the sequenceand indicates a move from “accessory mode” back to “stop mode”. Sincethe valves are set to a low power consumption mode during the T3interval, the mode request change at marker 1607 does not alter thestate of the valves.

Thus, FIG. 16 illustrates that it is possible to prepare an engine forstart by pre-positioning valves while in the “accessory mode” withouthaving to continue to drain power from the battery to keep the engine ina ready state. Further, the operator can make more than one transitionfrom “stop mode” to “accessory mode” without exposing the operator tovalve noise every time the transition is made. Further still, it ispossible to reduce power consumption if the operator leaves the vehiclein the “accessory mode” for an extended period of time.

Note that the logic of FIG. 15 may be made so that the timer is reset ateach transition from “accessory mode” to “stop mode” or so that thetimer in step 1509 is reset only after a predetermined amount of timehas expired, for example.

The valve trajectories of FIG. 16 illustrate one example valve controlsequence of the method described by FIG. 15. In addition, it is possibleto extend this valve control to other types of variable eventvalvetrains, electro-hydraulically actuated valves for example.

Referring now to FIG. 17, a flow chart of an example turbo chargercontrol strategy for an engine having a variable event valvetrain isshown. Block 1701 represents the demanded boost pressure. The boostpressure is the pressure in the intake manifold between the compressorand the throttle body. The commanded boost is a function of the desiredengine torque (Tor_(des)), engine speed (N), atmospheric pressure(P_(atm)), and the desired intake manifold pressure (P_(man) _(—)_(des)). Where the desired engine torque is found from the sum of theoperator requested brake torque, engine friction torque, and the engineaccessory torque, for example. Engine brake torque can be determinedfrom a pedal command, for example, while friction and accessory torquesmay be determined from empirical data that may be stored in tablesand/or functions that may be related to engine speed, for example.Further, the commanded boost pressure may include compensation for theturbo charger compressor map, turbine characteristics, and enginepumping losses.

The commanded boost pressure minus the measured boost pressure is passedfrom the summing junction between blocks 1701 and 1703 to block 1703.This is a boost pressure error that control block 1703 operates on tocompensate for differences between the desired and actual measured boostpressure. Block 1703 may provide boost pressure compensation based on aproportion of the boost error, a proportion and integration of theerror, an estimate of system states that may be estimated from the boostdemand and the boost feedback, or by using other known techniques. Theterm K_(Bst)(Z) is used to describe the control gain of this particularblock and that the gain is based on a discrete system. Note that thegain of block 1703 may be linear, piecewise linear, and/or non-lineardepending on control objectives and the magnitude of the boost pressureerror. In other words, the boost gain may be set in a variety of ways todeliver the desired response.

The output of block 1703 is subtracted by the pressure from exhaustpressure symbolized by block 1707. The exhaust pressure may be directlymeasured or it may be inferred from engine speed, boost pressure,atmospheric pressure, air flow through the engine, and turbo chargervane or waste gate position, for example.

Controller gain block 1705 provides additional gain to the system inresponse to the output of the summer between blocks 1703 and 1705. Thecontroller gain of block 1705 may be constructed by any of the methodsmentioned above for block 1703. Gains of blocks 1703 and 1705 areselected to consider the desired response and desired stability of thesystem. The output of gain block 1705 is used to command the turbocharger vane or waste gate positioning device and can affect the outputof the turbo charger compressor. The compressor boost pressure ismonitored by a pressure sensor at block 1709 and provides an indicationof the compressor flow rate.

The commanded intake manifold pressure is determined in block 1710.Intake manifold pressure can be determined by using tables or functionsthat are combined to output a manifold pressure that incorporatesadjustments for engine noise, vacuum request of ancillary systems (e.g.,brake boost), boost pressure, engine speed, desired torque, and enginevolumetric efficiency, for example.

At block 1713 the difference between the desired intake manifoldpressure P_(man) _(—) _(des) and the measured manifold pressure (block1715) is operated on by a gain adjustment factor. The gain adjustmentmay be configured as any one of the types mentioned in the descriptionof block 1703 and operates on electronic throttle controller 1717. Ofcourse, the position of the electronic throttle plate affects the intakemanifold pressure and therefore can affect the timing of variable eventvalvetrain valves because the valve timing is dependant, in part, onintake manifold pressure. Therefore, the intake manifold pressure isused as a factor in determining valve timing. In one example, the valvetimings may be determined as a function of the desired engine torque,intake manifold pressure, residuals (i.e., combusted air and fuel), andengine speed. Specifically, intake valve opening (IVO), exhaust valveclosing (IVC), and exhaust valve opening (IVO) can be determine fromempirically determined values that can be stored in tables that areindexed by engine speed and air flow through the engine. Intake valveclosing may then be determined by calculating the cylinder volume at agiven intake manifold pressure that corresponds to the desired cylinderair charge. That is, the intake valve closing location can then bedetermined to be the crankshaft angle where the intake valves are closedso that the cylinder volume at the prescribed valve closing yields thedesired cylinder air charge. In addition, the desired cylinder aircharge and therefore the valve timing can be adjusted at a rate thatrestricts the air flow through the engine to be less than or equal tothe air flow through the compressor turbine at the time the valveadjustment is made. For additional description of a method to determinevalve timings see the previously referenced U.S. patent application Ser.No. 10/805,642, for example. The valves and throttle adjustments canchange the inducted cylinder air amount and therefore may be used toadjust the engine torque.

Thus, FIG. 17 illustrates an example of a method to adjust engine valvetiming for a turbo charge engine having a variable event valvetrain. Thegains Referring now to FIG. 18 a, a plot of signals of interest duringan increasing torque request of a turbo charged engine having a variableevent valvetrain is shown. Curve 1801 is a torque simulation response toa near step input torque demand request. The response is based on asystem that uses boost pressure feedback and that allows intake valvetiming to be adjusted to the limit of the valve actuator response. Theengine torque response increases until location 1803 where itmomentarily decreases and then increases again and then overshoots thedesired torque. The torque sag at location 1803 and the overshoot of thedesired torque can lead to drivability issues for the operator. In otherwords, the torque response of this system configuration may be felt bythe driver and may therefore affect the pleasure of the drivingexperience.

Referring now to FIG. 18 b, another plot of signals of interest duringan increasing torque request of a turbo charged engine having a variableevent valvetrain is shown. This plot is similar to the plot of FIG. 18a, but the torque response is improved by modifications to the torquecontrol system as described in FIG. 17. Specifically, the torqueresponse of curve 1805 increases monotonically from the change in thedemand torque and the overshoot is also reduced. This torque responsecan reduce the variation of vehicle acceleration and may also improvethe audible sound of the engine since the engine speed can also increasemonotonically as the engine torque increases. In other words, thedriver's perception of vehicle operation may be improved since thevehicle can accelerate in a steady manner. Further, transmissionshifting may be improved because the engine accelerates in a predictableway and because shifts during an unexpected torque reduction may beavoided.

Referring now to FIG. 19, a flow chart of an example valve releasestrategy during an engine stop is shown. In step 1901, the routinedetermines if an engine stop has been requested. As mentioned above, anengine stop request may be initiated by an operator or by anotherpowertrain system, for example. If an engine stop has not be requestedthe routine exits. If an engine stop has been requested the routineproceeds to step 1903.

In step 1903, the routine evaluates a series of status registers thatcontain an indication of the current stroke of each cylinder (e.g.,power stroke, combustion stroke, intake stroke, etc.) to determine therespective stroke each cylinder is on at the present engine stopposition. The routine proceeds to step 1905.

In step 1905, the routine determines if the engine rotation has stopped.If so, the routine proceeds to step 1907, if not, the routine returns tostep 1903.

In step 1907, a group of valves is opened at a controlled rate so thatthe pressure difference between the exhaust manifold and the cylinder orbetween the intake manifold and the cylinder is slowly reduced.Alternatively, where the valves are comprised of permanent magnets,power may be reduced to the valve at a controlled rate until power flowis stopped, thereby releasing the valve, although the position of avalve having permanent magnets may not change after valve release.Conversely, if the valve is in a full open position at engine stop thevalve can be slowly released to the neutral position so that valve noiseis reduced. Also, a valve group may be comprised of one or more valvesand may be further comprised of different types of valves, intake orexhaust valves for example. Further still, a group of valves may becomprised of both intake and exhaust valves. Thus, valves may be openedor closed during an engine stop at rates and in sequences that aredifferent than those used during running engine conditions.

The valves in a group may be released simultaneously or they may bereleased at individual times or a predetermined number of valves may bereleased at a predetermined time. Further, the valve release rate may bebased on the pressure in a cylinder or in another embodiment the valverelease rate may be based on the pressure in the cylinder. Note thatcylinder pressure may be measured or estimated from the position of thepiston in the cylinder and by the cylinder stroke. If the piston of acylinder holding trapped exhaust gases stops at a location where thevolume of the cylinder is one half of the available cylinder volume thenthe valve may be released at a first rate. On the other hand, if anothercylinder contains a small air amount that is slightly pressurized thenthe valve operating in this cylinder may be released at a second rate, arate higher or lower than the first rate, for example. Valve releaserates are typically in units of millimeters per second. The routineproceeds to step 1909.

In step 1909, a second group of valves can be released. This group ofvalves may be released in any one of the previously mentioned waysdepending on desired results. In addition, there may be a delay betweenreleasing the first group of valves and releasing the second group ofvalves. The routine proceeds to exit.

Note that it may be necessary to first decrease current to the valve andthen to increase current to the valve so that a desired valve positionmay be achieved during a valve release operation. This occurs becausefor the same amount of spring force additional current is required tohold valve in place as the distance increases from the face of theelectro-magnet to the armature plate. Further, as mentioned above, avalve may be released by stopping current flow to the valve without thevalve actually moving. This case may occur for valves that havepermanent magnets that can balance the valve opening spring force.

Referring now to FIG. 20, a plot of an example valve release at enginestop is shown. Intake and exhaust valve trajectories for a four cylinderengine are illustrated similar to those shown in FIGS. 6-8. At location2001 a request to stop the engine is made. The engine may be stopped bystopping fuel flow to the cylinders. The intake and exhaust valvescontinue to operate in a four stroke manner, but valve operation may bealtered after the request to stop so that engine emissions may bereduced, for example. Note as an alternative, the intake and/or exhaustvalves may be controlled during an engine shutdown or start by any ofthe above mentioned methods or by a method described in any of theincorporated by references.

The engine reaches a stop at location 2003. The engine remains stoppedin region 2005 until it is restarted at location 2007. The stop durationmay vary in length of time and as such the duration illustrated in FIG.20 is not meant to limit the breadth or scope of the description. Inaddition, it is also possible to begin releasing the valves any timeafter the request to stop the engine has occurred. For example, valvesmay be released after an engine stop request at a predetermined time,after a predetermined amount of engine rotation, or at a predeterminedamount of time after the engine has stopped rotating.

In FIG. 20, the intake valve of cylinder three is in an open position atengine stop. The figure shows that the valve trajectory moves at acontrolled rate from the open position to the closed position. Thisexample trajectory can reduce the amount of valve noise since the valvehas fewer tendencies to bounce between magnets at engine stop. Thefigure shows exhaust constituents of cylinder three, from a priorcombustion event, being released prior to opening the intake valve sothe intake valve of cylinder three may be released with less concern ofreleasing exhaust gas into the intake manifold. The exhaust valves forcylinders one through four are released at locations 2011, 2013, 2015,and 2017. Cylinder one and cylinder two exhaust valves begin movementtoward the neutral position at substantially the same time and atsubstantially the same rate. Cylinders three and four exhaust valvesbegin movement shortly after engine stop and at a different rate thanthe exhaust valves of cylinders one and two. Thus, the figure showsdifferent valves being released at different times, at different releaserates (i.e., the rate at which the valve opens, 0.1 mm/sec for example),and with different groups of valves. By staggering the valve releasetime along with the valve release rate it is possible to reduce thevalve noise as well as noise from gases escaping or entering thecylinders. Further, by slowly releasing valves at different times theinstantaneous current draw may be reduced. Further still, selectedvalves can be released based on the contents of the cylinder and/or theposition of the piston in the cylinder so that the cylinder contents arereleased to the manifold suited for the cylinder contents. For example,it is possible to intake an air-fuel mixture, combust the mixture, andthen be at an engine stop position where the mixture is pressurized andtrapped in the cylinder. In this condition the contents of the cylindercan be released to the exhaust manifold at a controlled rate so that theexhaust constituents are at least partially converted by the warmcatalyst, thereby reducing engine emissions. On the other hand, for acylinder that has inducted an air charge but that has not combusted itmay be desirable to exhaust the cylinder contents to the intake manifoldso that the fresh air does not cool the exhaust catalyst, for example.

As will be appreciated by one of ordinary skill in the art, the routinesdescribed in FIGS. 4-5, 9-12, 15, and 19 may represent one or more ofany number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various steps or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the objects,features, and advantages described herein, but it is provided for easeof illustration and description. Although not explicitly illustrated,one of ordinary skill in the art will recognize that one or more of theillustrated steps or functions may be repeatedly performed depending onthe particular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1. A method for stopping an engine having a variable event valvetrain,the method comprising: stopping said engine; adjusting the current flowto at least a valve actuator to control the rate a valve is moved to aposition by said valve actuator.
 2. The method of claim 1 wherein saidrate increases with time.
 3. The method of claim 1 further comprisingmoving said valve from a first position to a second position at saidcontrolled rate.
 4. The method of claim 1 wherein said rate is an amountof valve lift per unit time.
 5. The method of claim 1 further comprisingdelaying the amount of time between said engine stop and moving said atleast a valve.
 6. The method of claim 4 wherein said time varies as anoperating condition varies.
 7. The method of claim 6 wherein saidoperating condition is an operating condition of said engine.
 8. Themethod of claim 6 wherein said operating condition is and operatingcondition of a vehicle, said engine operable in said vehicle.
 9. Themethod of claim 2 wherein said rate varies with operating conditions.10. The method of claim 1 wherein said valve actuator is comprised of atleast one permanent magnet.
 11. The method of claim 3 wherein said firstposition is a full open or a full closed position.
 12. A method forstopping an engine having a variable event valvetrain, the methodcomprising: stopping said engine; adjusting the current flow to at leasta valve actuator to control the rate a valve is moved to a firstposition by said valve actuator after said engine stop; and moving saidvalve actuator from said first position to a second position at anengine start.
 13. The method of claim 12 wherein said first position isa neutral position.
 14. The method of claim 12 wherein said firstposition is a closed position.
 15. The method of claim 12 wherein saidsecond position is an open position.
 16. The method of claim 12 whereinsaid second position is a closed position.
 17. The method of claim 12wherein said rate varies with operating conditions.
 18. The method ofclaim 12 wherein at least one of said first group of valves and at leastone of said second group of valves is an electrically actuated valve.